I. Field of the Invention
The invention relates to a low softening point petroleum pitch and scaler made from this pitch for asphalt pavement or metal surfaces.
II. Description of the Prior Art
There are two basic types of driveway or pavement sealer--coal tar based and asphalt based. These materials are primarily used to seal driveways and other pavement surfaces, but can also be used to seal or coat metal, wood, or cementitious surfaces, e.g., pipe coatings.
Coal tar is the premier product and has the largest market share. Driveway sealer made from coal tar is an emulsion of water, coal tar pitch, clay and water, perhaps with emulsifier and optional ingredients such as sand. These materials are long lasting, have a pleasing black color, and are resistant to gasoline and kerosene spills, but have an objectionable odor during application and contain aromatic compounds. Asphalt based materials are made from distilled petroleum fractions, typically vacuum tower bottoms or perhaps atmospheric tower bottoms. These heavy hydrocarbon fractions are sometimes oxidized or "blown" to change the asphalt properties. Asphalt based sealers do not smell as much as the coal tar based materials and are able to withstand a wider range of temperatures. The asphalt sealers are not as toxic and in some areas only asphalt-based sealers are sold. Asphalt sealers do not have the black color desired by many users. Asphalt sealers do not last as long, and frequently must be reapplied every year or every two years.
The goal of the present invention is to provide a low softening point pitch product similar to coal tar sealer base with similar physical properties such as viscosity and softening point. This material is intended to be a complete, or at least partial, replacement of coal tar, so that sealer base and driveway sealers with acceptable properties can be made with less, or no, coal tar pitch. With that goal in mind, some of the closest art known is reviewed hereafter. The art review can be arbitrarily grouped into four areas:
A. Coal tar driveway sealer PA1 B. Blends of coal tar pitch/petroleum PA1 C. Control of pitch production PA1 D. Low softening point pitches PA1 water, PA1 clay, PA1 emulsifier and PA1 "sealer base" or "binder". PA1 high softening point petroleum pitch which is a solid at room temperature and PA1 an aromatic rich cutback oil. PA1 FCC light cycle oil PA1 FCC slurry oil, or clarified slurry oil PA1 Coker naphtha PA1 Coker gas oil PA1 Aromatic extracts PA1 Cleveland Open Cup Flash (COC) of greater than 270-400.degree. F. PA1 Viscosity, Fural @ 122.degree. F. of greater than 20 seconds PA1 Broadly PA1 Preferred
Coal Tar Driveway Sealer
U.S. Pat. No. 4,222,916, Hergenrother, RUBBERIZED COAL TAR PITCH EMULSION, discloses a coal tar based sealer with acrylate emulsion.
U.S. Pat. No. 4,537,635, Bart et al., teaches driveway sealers from oxidized coal tar.
As stated previously, most driveway sealer is either a premium product based on coal tar or a coal tar free, asphalt based product, which lasts for a year. Blends of coal tar and asphalt based products are not sold commercially. An additional concern is that coal tar based driveway sealers comply with the specifications for coal tar based sealers disclosed in ASTM D3320, Emulsified Coal Tar Pitch (Mineral Colloidal Type), and Federal Specification R-P=355e, Pitch, Coal Tar Emulsion (Coating for Bituminous Pavements), which specify use of coal tar pitch. Although coal tar/petroleum pitch blends are not used commercially in driveway sealers, there have been reports of pitch blends for other uses, reviewed next.
Blends of Coal Tar Pitch/Petroleum
Commercial blends of coal tar pitch and a minor amount of petroleum pitch have probably been made. For aluminum anode binder pitch, reviewed in greater length hereafter, it has been common to "extend" the coal tar pitch by blending in up to 10% petroleum pitch, so that the pitch used was a 90:10 blend of coal tar:petroleum pitch. Some uses of petroleum pitch as an extender for driveway sealer may have occurred, but they have not been reported in the literature.
Blends of coal tar with petroleum pitch are known in the art, but not for driveway sealer. This art, reviewed hereafter, is believed to be the closest to the low softening point petroleum pitch of the present invention.
U.S. Pat. No. 5,746,906, McHenry, et. al., May 5, 1998, disclosed a coal tar pitch/petroleum pitch blend and method of making it. A crude coal tar material is selected according to specific properties including QI, specific gravity, water and ash content. A petroleum pitch material is also selected according to its softening point, QI, coking value and sulfur content. The coal tar pitch is distilled to an uncharacteristically high softening point then mixed with a lower softening point petroleum pitch to a desired softening end point. The material retains significant QI and coking value characteristics of pure coal tar pitch particularly for use in Soderberg-type anodes for aluminum smelting as well as electric arc furnace electrodes. PAH emissions, and more specifically B(a)P equivalent emissions, are all reduced by approximately 40%.
The petroleum pitch used in '906 had a softening point of 80.degree. C. nominal. This was mixed with coal tar pitch distilled to have a softening point of 130-175.degree. C.
Control of Pitch Production
Control of coal tar pitch fractionation is described in U.S. Pat. No. 4,066,159.
Control of petroleum pitch fractionation is straightforward distillation.
It is easy to run any pitch fractionation process to produce a product with the desired softening point and this is the norm for most pitches, both coal tar and petroleum.
Low Softening Point Pitch
Some coal tar pitch materials are made with a relatively low softening point. For driveway sealer use, the coal tar pitch will typically have a softening point of around 40.degree. C., as discussed in the driveway sealer art.
Petroleum pitches which are solids at room temperature, and which are not suitable for use as driveway sealer, have been made by producing a high softening point material, e.g., A240, and blending this with cutter stock such as aromatic oil. These blends are generally destined for use as a binder pitch or impregnant, and for these uses a highly aromatic solvent is preferred to increase coking value. Some physical properties of various commercial petroleum pitch products are summarized in the following section.
TABLE 1 Specifications and Typical Properties of Marathon Ashland Petroleum Pitch CAS Number 68334-31-6 Test A170 A240 A225 Analysis Method Pitch Pitch Pitch Specification Points Limits Softening Point, Mettler ASTM 79.4-82.6 118-124 105-110 .degree. C. D3104 Softening Point, Ring & ASTM 166-171 235-248 212-221 Ball .degree. F. D36 Flash, Cleveland Open ASTM 200 270 260 Cup, .degree. C. minimum D92 Coking Value, Modified Conradson Carbon, ASTM NA 49 46 wt %, minimum D2416 Sulfur Content, wt %, ASTM NA 3.0 1.5 maximum D1552 or D4294 Typical Properties Values Specific Gravity, Helium ASTM 1.18 1.22 1.22 Pycnometer, g/cc, D71 minimum Moisture, wt %, -- -- 0.5 -- maximum Toluene Insolubles, ASTM -- 2.10 2.10 wt %, minimum D4072 Quinoline Insolubles, ASTM D 0 0.5 0.5 wt % maximum 2318
The above pitches, all solids at room temperature, were made from a direct thermal process or blending A240 with an appropriate cutter oil. A pourable pitch product, one suitable for use in driveway sealers or industrial coatings, has been made from blends of A240 and #6 fuel oil. The driveway sealer usually contains a surfactant or other emulsifier, which would be expected to prevent phase incompatibility problems.
Art Summary
This voluminous art could be summarized as follows.
Driveway sealers are made from coal tar pitch (premium products) or asphalt, but not both. Blends of coal tar pitch and petroleum pitch are used for making anodes for aluminum production. Blends of high softening point petroleum pitch with aromatic oils have been made to produce materials which are solids at room temperature. Pourable petroleum pitch products have been made by blending high softening point pitch with fuel oil.
This pourable (pitch+fuel oil) blend can be further blended with coal tar and other conventional ingredients to produce a good driveway sealer for most markets. The sealers made from such pourable blends of petroleum pitch and fuel oil have two areas where further improvement would improve the market for the product. These two areas are durability and phase stability.
Durability refers to the ability of the driveway sealer product to withstand normal traffic--from feet, automobiles, and the other impacts to which road surfaces are subjected. The pure coal tar sealers have excellent durability, and typically last three years on a normal driveway. The blends, made from coal tar pitch and petroleum pitch+fuel oil, have a satisfactory but reduced durability as compared to the pure coal tar product.
Phase stability refers to the ability of the finished product (an emulsion) to stand for a long time without phase separation and to the ability of the sealer base--a blend of petroleum pitch with fuel oil preferably containing significant amounts of low softening point coal tar pitch--to be stable on storage.
The phase stability problem is relatively minor in terms of finished product--most driveway sealers contain emulsifier which helps keep the oil and water phases mixed. There is usually some settling of the clay. Some stirring is required. This is not to say that phase separation is not a problem, just that so much settles out that customers accept as inevitable the need to stir the product before using it, so breaking of the (petroleum pitch+fuel oil) emulsion is not significant.
Phase instability, in sealer base, can be catastrophic. The currently used blends of high softening point petroleum pitch blended with #6 fuel oil can, even when further blended with low softening point coal tar pitch, precipitate a bottom "tar" phase in the base of storage tanks and trucks. This tar phase can break impellers used to produce finished driveway scaler or seriously complicate the manufacturing process.
We discovered a way to prevent phase separation of sealer base made from blends of coal tar and petroleum. Use of aromatic rich oil will greatly reduce or eliminate phase separation of blended sealer base products. We also discovered an unexpected increase in durability of driveway sealer when aromatic rich oil, rather than a more aliphatic fuel oil, was used to dilute the petroleum pitch.